The present invention relates to an electric machine having a stator, a rotor comprising a shaft and provided with radial and axial cooling channels and acting as a rotor fan, and having an axial fan that is disposed coaxially with the shaft and delivers coolant into the axial cooling channels. The axial fan, for its part, has a first blade ring, which is enclosed by a funnel-shaped tube and is non-rotatably connected to the same. The smaller opening of the funnel-shaped tube is directly connected to the axial cooling channels of the rotor.
Electric machines of higher power rating must be equipped with effective cooling systems. High utilization of the electric machine can be achieved only with a powerful cooling system, if necessary a bilateral ventilation. In many cases, the rotor of an electric machine itself exhibits a certain fan effect when it is provided with radially extending channels. Axial channels that are connected to these radial channels provide for an air flow from the front sides of the rotor to the respective radial channels. The rotor then operates according to the principle of a radial fan. The thus produced air flow cools not only the rotor itself, but may also cool the laminated core of the stator.
The cooling effect of the rotor fan is determined by the air intake and outlet diameter, the fluid friction and dynamic pressure losses at disturbance sites in the rotor. One of these disturbance sites is the air intake of the typically stationary air into the rotating axial channels.
In order to optimize the fan effect of the rotor, hitherto attention has been paid only to keeping the axial on-flow area and the radial off-flow area in an appropriate ratio to one another, and otherwise not creating any unnecessary constrictions for the air, or the coolant. The air intake resistance is usually not optimized.
In order also to cool the winding overhangs of the electric machine, frequently an axial fan is mounted on the machine shaft, at a certain distance from the rotor front side. In order to avoid problems resulting from mutual influencing of the axial fan and rotor fan, there are embodiments in which the suction side of the rotor fan is separated from the pressure side of the axial fan by a tube, on which the hub of the axial fan is placed.
An electric machine of the generic type is known from the publication SU 147 30 18 A1. It has a stator laminated core and a rotor laminated core, each having radial cooling channels. The rotor additionally has axial cooling channels, in order to direct coolant from the front side of the rotor to the radial cooling channels. Arranged on the front side of the rotor is a ventilator having a funnel-shaped casing, which delivers the coolant into the axial channels of the rotor. The coolant flows out of the winding overhang space into the ventilator. Flowing past the winding overhang causes the coolant to become already heated before it flows into the ventilator, or rotor. Consequently, adequate cooling of the rotor cannot be ensured in all cases.
Furthermore, the publication DE 196 53 839 A1 discloses a rotor of a turbo-generator having direct gas cooling. Provided between a rotor cap plate and a rotor shaft there is a two-stage blade grid, for causing cooling air to flow onto the rotor and the rotor winding. The first blade grid stage in the direction of flow is a delay grid having pressure-generating characteristics, and the blade grid stage that follows in the direction of flow is a delay grid having deflection characteristics.
Furthermore, the publication DE 79 00 792 U1 discloses a self-ventilated electric machine. An axial fan serves to deliver a cooling air flow, which axial fan is arranged on a hollow hub whose inner diameter is greater than the diameter on which the axial cooling channels of the rotor are located. For mechanical stiffness, some ribs are provided between the hub and the rotor shaft.
Further, the patent specification DE 195 48 321 C1 describes a cooling device, particularly for turbo-generators. A cooler is connected, via delivery channels, to the rotor, in which cooling channels are realized for the purpose of cooling the conductor of the rotor. At least one blade ring is provided in at least one delivery channel, which blade ring imparts to the cooling fluid a tangential speed component in the direction of rotation of the rotor and thus promotes the flow of cooling fluid onto the rotor.
The object of the present invention consists in improving the cooling of an electric machine having radially extending cooling channels.